TOKYO (AP) — The operator of Japan’s crippled nuclear plant said today that it was moving tons of highly radioactive water from a temporary storage tank to another after detecting signs of leakage, in a blow to the plant’s struggles with tight storage space.

Tokyo Electric Power Co. said about 120 tons of the water are believed to have breached the tank’s inner linings, some of it possibly leaking into the soil. TEPCO is moving the water to a nearby tank at the Fukushima Dai-chi plant — a process that could take several days.

TEPCO detected the leak earlier in the week, when radiation levels spiked in water samples collected in between the inner linings of the tank. Radiation levels in water samples taken outside the tank also have increased, an indication of the water leak, TEPCO spokesman Masayuki Ono said.